Vacuum has traditionally been a primary motive force for many control functions within motor vehicles, particularly automobiles. Although electro-mechanical actuators have displaced vacuum motors for certain functions, vacuum remains the preferred method of modulating such automotive operating perameters as ignition timing, emissions control, throttle (cruise control) position and the like.
Ever increasing complexity required to conform with governmental regulations and added vehicle features have necessitated the addition of intelligence and sophistication to certain control functions. Even long standing, standard techniques of processing vacuum signals are being reexamined to wring out heretofor acceptable operating inefficiencies and to improve response characteristics. Such prior art approaches have typically been limited to dedicated, single function devices, such as a vacuum motor for modulating an exhaust gas recirculation (EGR) valve. Where added intelligence or complex processing is required, discrete separate components are generally coupled or cascaded to achieve the required processing capability.
A net effect of the increased complexity described above is that more intelligence or information is being modulated over a medium, typically engine vacuum in an automobile, of finite capacity. This phenomenon results in a control system which processes data having ever decreasing incremental differentiation. Restated, today's control systems must be capable of accurately distinguishing and responding to smaller and smaller changes in fluid pressure (ex. engine vacuum).
As a result of the requirement of increased information processing, fluid pressure control systems often have complex fluidic systems which, themselves, can constitute a restriction to system fluid flow which, in some modes of operation, will compromise performance by increasing response time. A colorary to the restriction problem posed by complex system fluidics is the increased volume of fluid involved which, itself, can increase response time when gross or coarse adjustments to system pressure are required. Although dump valves are well-known in fluid pressure control systems, they are typically limited to rapidly changing system pressure to ambient pressure (one atmosphere) rather than in a more limited, but rapid, pressure variation. Finally, dump valves themselves are often solenoid operated and are included in a system as an ancillary branch. Such arrangements represent only a limited improvement in response time by requiring actuation by a separately generated control signal.